Voltage controlled oscillators (VCOs) are well known in the art. The primary function of a VCO is to provide a frequency response output as a function of voltage input signal amplitude. Despite the numerous advantages associated with using a VCO to support frequency synthesis, one basic shortcoming is the need to set the VCO bias in order to establish a stable quiescent (Q) operating point. As will be appreciated, the noise performance of a VCO is greatly influenced by Q. Failure to properly set the VCO bias may result in the generation of additive noise during operation.
Traditional methods for VCO biasing rely heavily on mechanical and/or manual procedures. Such methods may include the steps of: monitoring the VCO output frequency in response to a given VCO control voltage, or monitoring the VCO control voltage at a given frequency response, and then mechanically adjusting or laser trimming a bias resistor within the VCO's bias network.
As will be appreciated, such manual tuning operations are typically labor intensive, expensive, and susceptible to environmentally induced variations such as temperature, humidity, altitude, etc. It would be extremely advantageous therefore to provide a self-biasing VCO.